1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Conventional wireless communication systems include one or more base stations, which may also be referred to as node-Bs, for providing wireless connectivity to one or more mobile units, which may also be referred to using terms such as user equipment, subscriber equipment, and access terminals. Exemplary mobile units include cellular telephones, personal data assistants, smart phones, text messaging devices, laptop computers, desktop computers, and the like. Each base station may provide wireless connectivity to one or more mobile units in a geographical area, or cell, associated with the base station. For example, a base station that operates according to a Universal Mobile Telecommunication System (UMTS) protocol may provide wireless connectivity to one or more mobile units in a cell associated with the base station over a wireless communication link.
Wireless communication links typically include one or more uplink channels and one or more downlink channels. A mobile unit may transmit voice and/or data information to the base station over the uplink channel. For example, the mobile unit may transmit voice and/or data information over a data channel (e.g., a dedicated physical data channel, DPDCH). The mobile unit may also transmit control information associated with the voice and/or data information over a control channel (e.g., a dedicated physical control channel, DPCCH). For example, the mobile unit may transmit transport format combination information (TFCI) in a TFCI field of the control channel. Release 6 of the Third Generation Partnership Project (3GPP) standard for UMTS defines an enhanced data channel feature (E-DCH) that is designed to increase the uplink system capacity. The E-DCH feature has tighter control of the overall received rise of thermal (RoT) and introduces hybrid automatic repeat request (HARQ) technology. The HARQ allows mobile units to aggressively take advantage of a fading channel by implementing physical layer retransmission and soft combining at a turbo decoder in the base station. An enhanced control channel (e.g., an enhanced dedicated physical control channel, E-DPCCH) is introduced to transmit control information associated with the enhanced data channel. For example, the control channel may transmit E-TFCI information and/or HARQ Retransmission Sequence Number (RSN) information. In system capacity performance analyses, the E-DPCCH channel represents overhead and is a negative factor that may reduce system capacity.
FIG. 1 conceptually illustrates a conventional wireless communication system 100 that includes one or more data channels 105 and an enhanced data channel 107. In the illustrated embodiment, one or more data channels 105 may be used to transmit voice and/or data information according to the 3GPP '99 standard. The data channels 105 provide voice and/or data information to a coder and/or multiplexer 110, which encodes and/or multiplexes the information and provides the encoded and/or multiplexed information to a demultiplexer and/or splitter 120 over a control channel 125 (e.g., a coded composite transport channel, CCTrCH). The encoded and/or multiplexed information transmitted over the control channel 125 may also include signaling information. The demultiplexer and/or splitter 120 may then demultiplex and/or split the received information and provide it to one or more physical channels 130 for transmission over an air interface. Signaling information such as transmit power control (TPC) information and/or TFCI information may be transmitted over a signaling channel 135. Signaling information for the HARQ protocol, such as acknowledgment/negative-acknowledgment (ACK/NAK) bits and/or channel quality information (CQI) may be transmitted over a signaling channel 140.
The enhanced data channel 107 may be used to transmit voice and/or data information according to Release 6 of the 3GPP standard. The enhanced data channel 107 provides voice and/or data information to a coder and/or multiplexer 145, which encodes and/or multiplexes the information and provides the encoded and/or multiplexed information to a demultiplexer and/or splitter 150 over a control channel 155 (e.g., a CCTrCH). The encoded and/or multiplexed information transmitted over the control channel 155 may also include signaling information. The demultiplexer and/or splitter 150 may then demultiplex and/or split the received information and provide it to one or more physical channels 160 for transmission over an air interface.
Release 6 of the 3GPP requires one coded composite transport channel (CCTrCH) for the data channels 105 and another CCTrCH for the enhanced data channel 107. Thus, enhanced TFCI information for the enhanced data channel 107 is provided over a signaling channel 165 (e.g., an E-DPCCH channel). The signaling channel 165 also carries the RSN information for the HARQ operation. Since the E-DCH feature is designed to increase the efficiency of the radio resource utilization and the system capacity, the usage of the DCH is envisioned to greatly decrease. For example, voice-over-Internet-Protocol (VoIP) and/or streaming services may be provided over E-DCH and so the E-DCH may be better suited to carry some or all of the traffic that is conventionally carried by the DCH.